A modern hybrid-electric vehicle (‘HEV’) employs control devices and wiring circuits having a variety of electrical devices to control and manage flow of electrical power between electrical power storage devices and electrical power generators, including internal combustion engines and regenerative braking systems. Early, accurate detection and diagnosis of a malfunction in a component of the electrical system is important to ensure optimum performance of the HEV. One electrical circuit of interest comprises a power transmission circuit flowing pre-flux current between an electrical energy storage device and an electrical load, e.g. a DC/DC electrical converter. Other circuits of interest include parasitic loads such as electrical power steering or electrical power brakes. A typical circuit contains a power relay that permits flow of electrical power from the energy storage device to the electrical load. A failure of a power relay may reduce the ability of the vehicle to function in hybrid mode, thus affecting fuel economy and performance. Detection of a stuck-open power relay is readily achievable through known means, but detection of a stuck-closed power relay is more challenging to diagnose during ongoing operation of a hybrid electric vehicle.
A typical electrical power relay failure mode in stuck-closed position comprises an action wherein the relay contacts are welded together. Methods to detect stuck-closed failure typically include intrusive methods, which interfere with ongoing operation.
Therefore, what is needed is a method for regularly monitoring a power relay to detect a stuck-closed condition that does not interfere with ongoing vehicle operation, and able to be executed regularly and consistently.